I want to be able to display rates for each hotel in the form of a bar graph, similar to kayak and hipmunks price graph for flight search.
Based on your question, I would presume that you are relatively new to the travel technology space. Given that, my recommendation would be to go with the simplest approach and that is to use an online travel agency (OTA) API for pulling rates. Expedia's Affiliate network, for example, provides you with a nice API with rates and availability for their partner hotels. There is no cost for this except for your integration cost, of course. Once you prove your model and show some traction, you'll have a better chance of working out a better connectivity deal or even direct deals with the hotel brands. Remember that Hipmunk started out by using the Orbitz API for their flight data, so this is a totally valid way to start.